Brief Introduction On Checksum And Protocol

Jun 25 • General • 2435 Views • No Comments on Brief Introduction On Checksum And Protocol










A checksum is a type of redundancy check used to detect errors in a data.

Errors that frequently occur in a data when written to a disk, transmitted across a network or even if manipulated. These errors are very small for example for single incorrect bit but such small errors can  affect the quality of data and even make it useless. In the simplest way a checksum is created on calculating the binary values in a packet or block of data using some algorithm and storing the results with the same data.


Network layer is getting service from the data link layer .Network layer is interested in getting messages to a corresponding network layer module on an adjacent machine.

This remote Network Layer should receive the identical message generated by the sender .The Network Layer then should be sure  that all messages that it  sends, will be delivered error free.

The Network Layer demands that  messages to be delivered to the remote peer should be of exact  order as they are sent.

Due to which the ISO came up with a reference model which suggests that the data link layer would provide services to send the correct message which will be verified by the protocols  .

Protocol is of two kind-

  1. Noiseless channel
  2. Noise channel

Noiseless channel protocol

Here two paths have been introduced  one that uses flow control and the other that does not use any flow control.

It is of two types- simplest  and stop & wait protocol.

Simplest Protocol

It is the simplest form of. In this protocol the receiver

indicates that it is  ready  to receive data for each frame.It works on simple  Operations:

1. Sender-Transmits a single frame

2. Receiver: Transmits the acknowledgment (ACK)


Stop and wait protocols

In this case the  Frames have 1-bit sequence numbers (SN = 0 or 1) and the Receiver sends an acknowledgement (1-SN) if frame SN is correctly received, then the sender   waits for an ACK (1-SN) before transmitting the next frame with sequence number 1-Sn and If sender does not receive anything before a timeout value expires and it retransmits frame SN


Here there are disturbances in each path due to which acknowledgement is is of three types-

  • Stop-and-Wait ARQ
  • Go-Back-N ARQ
  • Selective ARQ


Go-Back-N Automatic Repeat Request

Go-Back-N ARQ  uses the sliding window type of protocol. When no errors are found the operations are identical to Sliding Window.


  • A station can send multiple frames as allowed by the window size
  • Receiver sends a NAK i provided  frame i  has error. After this the receiver discards all incoming frames unless the frame in error was correctly retransmitted
  • If sender receives a NAK i it will retransmit frame I and all packets i+1, i+2,… which have been sent, but not been acknowledged.

Selective repeat request

Similar to Go-Back-N ARQ here  the sender only retransmits frames for those which a NAK is received

Advantage over Go-Back-N:

  • Less  Retransmissions.


  • High amount of  complexity at sender and receiver
  • Each frame should be acknowledged individually (no cumulative acknowledgements)
  • Receiver  receives frames out of sequence

questions and answers

1. Name the network support layers?

Ans- The network support layers are the data link layer and physical layer. the user support layers?

ans- the user suppor layer are the session layer,presentation layer and application layer.

3.define supernetting?

ans-combination of many neworks into a large one.

4.What is protocol?

ans- set of rules governing the communication system.

5.What is the use of ISOC?

ANS- promotion of research activities.

GATE Syllabus-

1. Gate syllabus for Electronics and Communication Engineering

2. Gate syllabus for Computer Science and Information Technology

IES Syllabus-

1. IES Syllabus for Electronics and Telecomm

2. IES Syllabus for General Ability


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